1. Field of the Invention
The present invention relates to a composition for diagnosing, treating, and preventing liver disease, more precisely, a composition for diagnosing liver disease comprising a material for measuring TM4SF5 (Transmembrane 4 L six family member 5 or Four-Transmembrane L6 Superfamily member 5) protein grade, a kit for diagnosing liver disease containing the said composition, a method for providing information for diagnosing liver disease which is characterized by measuring the grade of TM4SF5 protein and the expressions of TM4SF5 expression related signaling proteins and the grade of phosphorylation to compare with those of the normal control group sample, a method for screening a material for treating liver disease, and a composition for treating or preventing liver disease containing a material inhibiting the expressions of TM4SF5 protein and TM4SF5 expression related signaling proteins and phosphorylation as well.
2. Description of the Related Art
The liver is a very important organ that is functioning in relation to many mechanisms in our body including lipid metabolism, detoxification, biliary excretion, storage of various nutritions, hematosis, blood clotting, regulation of circulating blood volume, etc. Therefore, once the liver is damaged, many functions become weak and if the damage or disorder gets worse, life itself will be in danger.
Functions of the liver are described hereinafter in more detail. First, the liver is functioning to control energy metabolism. That is, every nutrient absorbed from food is metabolized into energy producing materials in the liver, which are supplied to every part of the whole body or stored therein. Second, the liver is functioning to synthesize approximately 2,000 kinds of enzymes, serum proteins such as albumin and coagulation factors, bile acid, and lipids such as phospholipid and cholesterol, and store and distribute them as well. Third, the liver has detoxification and decomposition activities. Particularly, the liver is functioning to detoxify drugs, alcohol, and other toxic materials, because of which the liver is easily damaged, leading to drug-induced, toxic, and alcoholic liver diseases. In addition, the liver is involved in the excretion of metabolites to the duodenum and also involved in immune system, suggesting that the liver plays an important role in maintaining life system.
Liver disease is classified into viral liver disease, alcoholic liver disease, drug-induced toxic liver disease, fatty liver, autoimmune liver disease, metabolic liver disease, and other liver disease according to the cause. Liver disease does not show any subjective symptoms in the early stage. Only when the liver disease is already progressed, it is detected. Therefore, liver disease is the top reason of death not only domestically but also world-widely, requiring the development of an effective diagnosis and treatment method.
When the liver gets stimuli such as alcohol, virus, and other toxic environmental factors, hepatic stellate cells become activated to secret various cytokines including TGFβ. In particular, TGFβ (transforming growth factor β) is a multi-functional cytokine which has been known to play a critical role in development and carcinogenesis. In TGFβ signal transduction system, TGFβ receptor is activated by TGFβ, and the activated TGFβ receptor induces phosphorylation and activation of intracellular Smad2/3 protein. Then, the receptor is conjugated with Smad4, which is transferred into nucleus to cause transcriptions of related genes.
The secreted TGFβ accelerates collagen synthesis to induce hepatic fibrosis and to affect not only hepatic stellate cells but also surrounding hepatocytes to cause EMT (epithelial to mesenchymal transition). The continued hepatic fibrosis results in liver cirrhosis in the end. Thus, it is a very basic step to study and understand hepatic fibrosis process in order to understand any possible reason to cause liver cirrhosis.
Alcoholic hepatic injury is caused by those compounds generated by alcohol itself or alcohol metabolism, which causes lipidosis, hepatic injury, and hepatic fibrosis. When hepatocytes are injured by various reasons such as alcohol, chronic hepatitis B, chronic hepatitis C, chronic autoimmune disease, chronic biliary disease, chronic heart disease, parasite, and drug addiction, etc, various cytokines and oxygen free radicals are generated by the interactions of hepatocytes, Kupffer cells, sinusoidal endothelial cells, and hepatic stellate cells (HSC), leading to the damage of normal extracellular matrix (ECM). Furthermore, abnormal proliferation of ECM such as collagen I and collagen III progresses to hepatic fibrosis. Unlike liver cirrhosis, hepatic fibrosis is reversible and is composed of thin fibril without nodule formation. Once the cause of hepatic injury is eliminated, hepatic fibrosis becomes reversed to normal. However, hepatic fibrosis is continuously repeated, crosslinking between ECM increases to form thick fibril, resulting in irreversible liver cirrhosis with nodules. The increase of ECM such as collagen is an important reason of hepatic fibrosis which is produced by HSC activated by various reasons.
As hepatic fibrosis is more progressed, liver cirrhosis is developed. Once hepatic necrosis occurs by any reason, hepatic regeneration and fibrosis are developed. If those processes are repeated continuously, liver cirrhosis is developed. Liver cirrhosis, which is formed by hepatic nodules developed by continuous or repeated diffused hepatic injury, fibrosis and hepatic regeneration, is a chronic disease accompanied by necrosis, inflammation, and fibrosis, which eventually progresses to even fatal liver cancer.
TM4SF5 (Four-Transmembrane L6 Superfamily member 5) known as a kind of tetraspanins (or tetraspan) is a water insoluble protein, which is structured by four transmembrane regions, two extracellular rings, one intracytoplasmic ring, and two terminal regions. TM4SF5 proteins form conjugates with cell adhesion molecules such as integrin on cell membrane to form a huge tetraspanin-web or tetraspanin-enriched microdomain (TERM), contributing to various biological functions such as cell adhesion, cell proliferation, and cell migration, etc. It has been known that TM4SF5 is over-expressed in human liver cancer cells and is functioning as a carcinogen by inducing the accumulation of p27kip1 protein in cytoplasm and accordingly inhibiting RhoA protein activity, leading to EMT and contact growth inhibition.
However, it has not been disclosed yet how TM4SF5 expression is induced by which signal transduction pathway, and how TM4SF5 is related to liver disease that progresses hepatic fibrosis and liver cirrhosis. Therefore, the present inventors investigated and confirmed that TGFβ induced TM4SF5 expression in the progress of liver disease and further completed this invention by confirming that TM4SF5 could be used as a marker for the diagnosis of liver disease and TM4SF5 antagonist could be used for the prevention and/or treatment of liver disease.